GPRS (General Packet Radio Service) that is currently being specified by ETSI (The European Telecommunication Standards Institute) as a service for GSM phase 2+, provides packet switched connections throughout the PLMN (Public Land Mobile Network). The packet switching is performed between the nodes in the network and on the radio interface. Packet traffic may exist between external data networks and mobile stations and between mobile stations. As in other mobile telephone systems, the mobile stations have radio access to the system with a minimum of consideration of how networks are built and which operators that owns them. They may be connected to an operator anywhere in the home country or somewhere abroad and switch country or operator according to their own needs or decisions.
To provide an efficient transfer of packets between the end users (payload) and also for control signalling between the network elements in the PLMN and the mobile station, layered protocols are used. Each layer or control function has its dedicated functions. Identification of a particular subscriber, either for transfer of payload or for control signalling, is normally done by an identification element that e.g. is a part of the header field in each packet or the first packet in case of segmented packets.
The architecture of GPRS is shown in FIG. 1.
The protocol stack for GPRS is sketched in FIG. 2.